The Internet country code top-level domain (ccTLD) .io is nominally assigned to the British Indian Ocean Territory.

[2] The .io domain was delegated by the Internet Assigned Numbers Authority (IANA) to British entrepreneur Paul Kane in 1997 together with the ccTLDs .ac (Ascension Island), .sh (St Helena), and .tm (Turkmenistan).

[6] In April 2017, Paul Kane sold the Internet Computer Bureau holding company to privately held domain name registry services provider Afilias for $70.17m in cash.

[8] In December 2020, Afilias' owner Hal Lubsen sold it to privately held Donuts for an undisclosed sum.

[9] One month later, in January 2021, Donuts was acquired by private equity firm Ethos Capital, again for an undisclosed sum.

[7][15][16] In October 2024, the United Kingdom announced that it would eventually cede the British Indian Ocean Territory to Mauritius, while maintaining the military base on Diego Garcia via an initial 99-year lease.

[19] The deal was put on hold following the 2024 United States presidential election to allow consideration from the new incoming administration.

(Since there are no legal, permanent inhabitants of the British Indian Ocean Territory, theoretically no third-level domains will be registered.)

.io domains are often used for open source projects, application programming interfaces ("APIs"), startup companies, browser games, and other online services.

Characterised by simple graphics and gameplay in a free for all multiplayer arena, .io games received around 192 million visits in 2017.